The present invention relates to semiconductor manufacturing, and more particularly to an apparatus for detecting the presence of a carrier in which semiconductor substrates are stored and/or transported.
Semiconductor devices are made on substrates, such as silicon wafers or glass plates, for use in computers, monitors, and the like. These devices are made by a sequence of fabrication steps, such as thin film deposition, oxidation or nitration, etching, polishing, and thermal and lithographic processing. Although multiple fabrication steps may be performed in a single processing station, substrates must be transported between processing stations for at least some of the fabrication steps.
Substrates are stored in open cassettes or sealed pods (hereinafter referred to collectively as xe2x80x9csubstrate carriersxe2x80x9d) for transfer between processing stations and other locations. Although substrate carriers may be carried manually between processing stations, the transfer of substrate carriers is typically automated.
Placement of a substrate carrier precisely at a predetermined position and alignment on a processing station or storage location may be of critical importance, particularly when the substrate carrier is to be removed from the processing station or storage location by an automated device, or when a substrate-handling robot is to remove substrates from the substrate carrier. To accommodate the need for precise and automatic placement of substrate carriers at processing stations and storage locations, an organization referred to as xe2x80x9cSEMIxe2x80x9d (Semiconductor Equipment and Materials International) has prescribed standards for three locator or alignment pins to be provided on processing stations or storage locations, and for corresponding slots provided on the bottom of substrate carriers. Locator pins and carrier slots provided in accordance with this standard operate to kinematically position substrate carriers in a precise and predetermined manner on processing stations or storage locations.
It is also known to provide sensors adjacent to the locator pins to allow for automatic detection of the presence of a substrate carrier at a processing station or storage location. The sensors are also employed to detect failure of the substrate carrier to seat properly on the locator pins. Because there are a number of ways in which a substrate carrier may be improperly positioned relative to the three locator pins called for by the SEMI standard, conventional practice to accurately determine positive carrier placement calls for providing at least five sensors at various positions near the three locator pins.
It would be desirable to provide an arrangement in which proper positioning of a substrate carrier on the three locator pins can be reliably detected using fewer than five sensors.
The invention comprises a wafer carrier locating pin having an integrated wafer carrier sensor. According to an aspect of the invention, the apparatus includes a surface adapted to receive the substrate carrier and a pin body mounted on, and extending upwardly from, the surface. The pin body has a slot formed therein. The apparatus also includes a paddle mounted in the slot of the pin body. The paddle is adapted to be actuated in a downward direction when the substrate carrier is seated on the pin body.
The pin body may have an uppermost point, and the paddle may be movable between a first position and a second position, with the paddle being held in the first position when no substrate carrier is present. According to this aspect of the invention, the paddle does not extend above the uppermost point of the pin body when the paddle is in the first position. The paddle may extend horizontally outwardly in two directions from the uppermost point of the pin body when the paddle is in the first position.
The pin body may have a rounded top and the paddle may be arranged so that it does not extend above any portion of the rounded top of the pin body when the paddle is in the second position.
The apparatus may further include a plunger held inside the pin body and coupled to the paddle for movement in a downward direction when the paddle is actuated. There may also be included in the apparatus a through-beam sensor mounted below the shelf. The through-beam sensor projects a beam that is adapted to be broken by a lower end of the plunger when the paddle is actuated. The apparatus may further include a spring adapted to bias the plunger and the paddle in an upward direction.
In an alternative embodiment of the invention, a through-beam sensor may be mounted adjacent the pin body in a recess of the surface. An actuator may be coupled to the paddle and adapted to break a beam of the through-beam sensor when the paddle is actuated.
According to another aspect of the invention, a station for receiving a substrate carrier is provided. The station includes a surface and three pins mounted on the surface. The three pins define a circle having a center point and each of the pins has a paddle mounted thereon. The paddles are actuatable by a substrate carrier placed on the surface and each paddle is substantially planar and defines a respective plane. Each paddle is mounted on the respective pin such that the plane defined by the paddle is substantially perpendicular to a line extending between the respective pin and the center point of the circle.
By integrating a carrier-sensing device with each locator pin, and arranging the sensing devices such that the sensing devices are actuated only when the pin is correctly engaged in the corresponding slot on the bottom of the carrier, the present invention permits reliable sensing of the correct positioning of the substrate carrier while, in one embodiment, using only three sensors. Thus, in this embodiment the sensing capabilities of a processing station or storage location may be provided at lower cost than conventional substrate carrier sensing arrangements.
Further features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.